I am at a loss as to why my 9" trac loc rear end is blowing oil out the vent tube so I am hoping someone might have a fix. I put a brand new Quicks Performance 9" rear end in my 65 Mustang last Spring with a trac loc 3.50 gears. The vent on the axle housing sits in the exact same place as the factory 8" rear end therefore I connected the hose exactly like it was done on the old rear end. I filled the differential until fluid started coming out the fill plug. I have driven the car at least 500 miles and gear oil is still coming out the vent and now I am worried I am low on fluid and will have to refill. I have been unable to figure out why it is doing this. I have no rear end noise. Does anyone have any suggestions as to how to fix this issue?
Probably over filled it. You actually want it so the fluid is just a tiny bit below the fill hole. Because of the high viscosity and surface tension in gear oil...if you fill it till it comes out of the hole it's actually slightly above the hole and you end up with an extra 1/2 or more quart.
When the oil gets hot it expands. I would wait until the hub is cold and check the oil level again. You should be able to fit your pinky finger in there and touch where the oil level is right below the hub plug opening.
Aside from what has already been suggested, I would ask what kind of gear oil you used. Recommended is GL-5 or GL-6. Automotive synthetic oils on the market today would be acceptable, but I would not recommend them for a new setup like yours. There is a lot of GL-2 floating around out there, and that stuff is for really heavy equipment. It foams up badly and could possibly be what is causing you to lose lube from the vent tube.